Restoration and Assessment of Water Resources of Drained Lakes. Example of Chełmno Lakeland (Poland)

Based on cartographic materials, three lakes drained in the previous centuries have been reconstructed. It was found that by restoring them to their original state their total surface area would rise by 140 ha. Knowing the water surface level, determined on the basis of the range of peat soils and contour lines, the author reconstructed the bathymetric plans of the lakes. This, in turn, allowed a determination of the volume of water stored in their basins. It amounted to ca. 2.5 million m³. The approach adopted in the paper draws attention to an important element, i.e., to lakes which no longer exist in Poland and which have disappeared as a result of hydrotechnical works. Their restoration to their original state could become an important link in water retention and delaying the land phase of the water cycle. Activities aimed at retaining water in reception basins are carried out in Poland, among others, through the small retention program. Within this project, facilities such as artificial storage reservoirs are being built. In the light of the foregoing, before making a decision to build such a reservoir, it is worth considering the possibility to restore the natural components of the environment, which is more justifiable, both from the point of view of subsequent functioning of the environment and economic factors.